The study of chemistry in aqueous micelles and other organized media has taken on a threefold importance as a tool for understanding a range of physiological chemistry. In vivo aggregation of surfactant like moleucles into micelles (bile salts, gangliosides, phospholipids and glycolipids) has been implicated as critical to the mode of action in a variety of receptors as well as digestive and transport functions. Secondly, substrate binding to surfactant aggregates has been viewed as a simplified model for the crucial interactions in enzyme-substrate and hormone-receptor complexes. Thridly, the ability of the more ordered surfactant vesicles to model both simple liposomes, and in turn membranes is also recognized. While some broad principles of the effect of such environments on chemical behavior have been delineated, little is known about the ability of oriented, hydrophobic media to selectively perturb chemical reactivity. Therefore, we propose a study of these interactions, using as a probe, systems whose basic chemistry is well understood. We suggest that these environments will have a profound effect on binding specificity, chemical reactivity and selectivity, and on both inter and intramolecular cooperativity. In some of the systems to be studied, we expect to exploit the possibility of cooperative action among surfactant head groups. A different approach will allow the hydrophobic region of the micelle to protect portions of a substrate while enhancing reaction elsewhere in the same molecule. We have also designed systems which give a fundamental calibration of the ability of the interfacial medium to affect reaction site specificity as well as nucleophilicity and basicity of bound ions and the balance between inter and intramolecular processes. We further expect to achieve both new chemistry and fundamental insight into these systems through the imposed organization and compartmentalization of both substrates and reagents. These systems are based on well precedented chemistry and their analysis involves a range of analytical techniques common to modern organic chemistry. We envision this approach as a major step towards ultimately applying chemical probes to even more complex interfacial environments.